Photographic processes



United S at s Pate PHOTOGRAPHIC PROCESSES Howard G. Rogers, Weston, Mass., assignor to Polaroid Corporation, Cambridge, Mass, a corporation of Delaware No Drawing. Application October 8, 1958 .Serial No. 765,925

'15 Claims. or. 96-29 This invention relates to photography and more particularly to processes for the development of photosensitive silver halide elements.

It is one object of the present invention to provide novel processes 'for the development of silver halide emulsions, in which the developing agent is capable of developing a photographic latent image and imparting a reversedror positive colored image of said latent image to a superposed image-receiving element.

A further object is to provide novelprocessessuitable I for use in preparing monochromatic and multichromatic photographic images. i

Other objects of the invention will inpart beobvious and will part appear hereinafter. I e g e The invention accordingly comprises the processes involving the several steps and the relation and order of one or more of such steps with respect to each of the others which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims. i V

U.S. Letters Patent Nos. 2,559,643 and 2,647,049 to Edwin H. Landdisclose examples of diffusion transfer reversal processes wherein aphotographic material, such as photosensitive element comprising an exposed silver halide emulsion layer containing a latent image,-is proc- .tioned patents to Edwin H. Land, and, in addition to developing the exposed silver halide emulsion, are effective to impart a positive dye image of the developed silver image to an image-receiving element, as will be -further described herein. These leuco compounds are the leuco derivatives of the product of the oxidative coupling of a p-phenylene ,diamine and a phenolic coupler, as described in detail hereinafter. They are particularly useful in providing the cyan component for a subtractive color process.v

In carrying out the process of this invention, a photosensitive element comprising a silver halide emulsion is exposed and a liquid processingcomposition applied thereto, as by immersing, coating, spraying, flowing, etc., l in the dark. 'In a preferred embodiment, thephotosensitive element contains a layer of the leuco compound,

and the liquid processing composition is applied to the exposed photosensitive element in a uniform layer as this element is brought into superposed relationship with an image-receiving element. .The liquid processing composition permeates the emulsion and provides a solution or leuco compound, substantially uniformly, "distributed-therein. As the latent image is developed,"

. the leuco compound is oxidized and immobilized in exposed areas. This immobilization isapparentlyprimarily due to a change in the solubility characteristics of the leuco compound upon oxidation, and especially as regards its solubility in alkaline solutions. The unoxidized leuco compound retains its solubility in the liquid processing composition, thereby providing an imagewise distribution of unoxidized leuco compound, at least part of which is transferred, by imbibition, to a superposed image-receiving element, said transfer substantially excluding oxidized leuco compound. The

latter element receives a depthwise difiusion, from the emulsion, of unoxidizedlleuco compound without appreciably disturbing its irnagewise distribution, thereby giving a reversed or positive, colored, image of the developed negative image. The image-receiving element may contain agents adapted to oxidize, mordant or otherwise fix the difiused, unoxidized leuco compound. Imbibition periods of approximately one minute have been found to give good results, but this contactperiod may be adjusted where necessary to compensate for variations in temperature or other conditions. The desired positive image is revealed by stripping the 'image-receivingelement from the photosensitive element at the end of the imbibition period. a

The leuco compounds or leuco dyes disclosed herein may be disposed in the liquid processing composition, in the image-receiving element, or in the photosensitive element; for example, in, on, or behind the silver halide emulsion layer. When. employed in either element the leuco dye becomes solubilized by the liquid processing composition as it permeates the element. In a preferred embodiment, a coating or layer of the leuco dye is incorporated in the: photosensitive element, preferably behind the silver halide emulsion layer, i.e., on the side of the emulsion adapted to be located most distant from ,the photographed subject when the photosensitive element is exposed. Placing the leuco dye behind the emulsion layer has the advantage of providing increased contrast in the positive image, and also minimizes any lightfiltering action if the leucodye is colored. If the leuco dye is colorless, it may be incorporated in the silver halide emulsion without adverse light-filtering effect.

Where the leuco dye is employed in a layer within the is to be applied to the emulsion by being spread thereon,

preferably in a relatively thin uniform layer, it may also include a viscosity-increasing compound constituting film-forming material of the type which, when spread over a water-absorbent base, willform a relatively firm and relatively stable film. Apreferred film-forming mal or sodium carboxymethyl cellulose.

terial is a high molecular weight polymer such as. a polymeric water-soluble ether which is inert to an alk-aline solution, as, for example, a hydroxyethyl cellulose Other film-forming materials .or thickening agents may be employed whose ability to increase viscosity is substantially unafiected when left in solution for a'long period of time.

The unoxidized leuco dye which diffuses to the imagereceiving element is oxidized to provide the desired positive dye image. This oxidation may be effected by merely exposing the stripped image-receiving element to the, air. In a preferred embodiment, the image rfeceiving element has incorporated therein an oxidizing Patented Oct. 20, 9

agent for the purpose of speeding up positive dye image formation and providing full image density immediately upon stripping. The incorporation of an oxidizing agent in the image-receiving element for the purpose of oxidizing unreacted developing agent permeated therein is described in the previously mentioned US. Patent No. 2,559,643. As examples of suitable oxidizing agents, mention may be made of peroxy compounds such as sodium or potassium perborate, certain dichromates such as ammonium dichromate, and compounds having polyvalent metallic elements in higher valent form such as copper, iron and cerium, wherein the metallic element is in higher valent form. Examples of these latter mentioned agents are cupric salts such as cupric sulfate. Another suitable oxidizing agent is benzoyl peroxide. Other useful oxidizing agents are quinones, and particularly 2,3-dicyano-1,4-benzoquinone.

As stated above, the leuco developing agents of this invention are the leuco derivatives of the products of the oxidative coupling of p-phenylene diamines with phenolic couplers. The products of such oxidative coupling are commonly referred to in the art as indophenols, but it should be noted that a more precise, although less used,- name is indoanilines. (See Synthetic Dyes, vol. II, K. Venkataraman, Academic Press, Inc., New York, N.Y., 1952, page 763.)

The leuco dyes of this invention may be represented by the formula a X-N-X wherein Y is a substituted or unsubstituted benzene or naphthalene ring containing a hydroxyl group para to I and nitrogen to which Y is attached, each Z may be hydrogen, alkyl, amino or alkoxy, X may be hydrogen or alkyl and each X may be the same or different. As used in this specification, alkyl is intended to include substituted alkyl groups, e.g., sulfonamido-alkyl groups. Y may also be substituted by halogen, alkyl, nitro, cycloalkyl, etc.

It is within the scope of this invention to use these leuco compounds as either the free base or as an acid addition salt, for example, the corresponding hydrochloride or oxalate.

.As specific examples of leuco dyes within the scope of this invention, mention may be made of the following:

2 chloro-4-(4'-diethylarnino-2'-methylanilino)-5 nitro-l-naphthol hydrochloride 2 chloro-4-(4-diethylamino-2'-methylanilino)-naphthol hydrochloride 2 chloro-4-(4'-diethylamino-anilino)-5-nitro-l-naphthol hydrochloride 4-(4-dimethylamino-anilino) -1-naphthol oxalate 4 (4-dimethylamino-anilino)-1-naphthol hydrochloride 2 chloro-4- [4'-(N-ethyl-N-beta methylsulfonamidoethyl) -amino-2-methoxyani]ino] -6-cyclohexyl-phenol hydrochloride 4 (4 dimethylamino-2-methylanilino)-5-nitro-1- naphthol hydrochloride 2 chloro 4-(4'-diethylamino-2-methylanilino)-5-ptoluene-sulfonamido-l-naphthol hydrochloride 2 chloro-4-[4-(N-ethyl-N-beta methylsulfonamidoethyl) -amino-2 -methoxyanilino] -5 -nit-rol-naphthol 2 chloro-4-(4-diethylamino-2-methylanilino)-5-nitro-l-naphthol 2 chloro-4-[4-(N-ethyl-N-beta methylsulfonamidoetgyl) amino-2'-methoxyanilino]-1-naphthol hydrochlon e 2 chloro-4(4-diethylamino-2'-propoxy anilino) 1- naphthol hydrochloride 2,4-diamino-4'-hydroxy-diphenylamine hydrochloride 1 (beta-methylsulfonamidoethyl)-5-(3-chloro-4-hydroxyl-l'-naphthylamino) 2,3-dihydroindole hydrochloride The following is an example of a use of the leuco dyes in accordance with this invention, and is given as an illustration only:

Example I A subcoated cellulose acetate film base is coated with a 4% aqueous gelatin solution. After this coating has dried, a coating is applied of a solution comprising 4 g. of 2-chloro-4-(4'-diethylamino-2-methylanilino)-5-nitrol-naphthol hydrochloride and 0.4 g. of p-N-benzylaminophenol in 100 cc. of a solution comprising:

Cellulose acetate hydrogen phthalate g 4 Acetone cc Methanol cc 20 Ethyl Cellosolve cc 1 A silver iodobromide emulsion is applied over the layer of leuco developing agent, after which the coated film base is exposed. The exposed, coated film base is wettcd with a liquid processing composition comprising:

Water 00.. Sodium carboxyrnethyl cellulose g 4.5 Sodium hydroxide g 2.0 Phenyl ethyl alcohol cc 1.5

'receiving element is separated and is found to contain a cyan, positive dye image of the photographed subject.

It will be noted that a conventional silver halide developing agent may be, and in the above example is, incorporated with the leuco dye. This conventional developer is preferably used in a quantity suflicient to accelerate development of the latent image. Use of such a developing agent has been found helpful in improving the tonal range or steps in the positive image. Some of the reacted leuco dye may be oxidized by an energy transfer reaction with oxidized auxiliary developing agent. The preferred auxiliary developing agents are those having a moderate developing potential. Among the developing agents which are preferred for this purpose are p-N-benzylaminophenol, ascorbic acid, p-anilino-phenol, l-amino-Z-naphthol, diethyl hydroxylamine and Metol (p-N-methylamino-phenol) It has also been found that hypophosphorus acid will improve the tonal range of the positive image obtained by the use of these leuco developing agents. An example of the use of hypophosphorus acid is:

Example 2 A photosensitive element is prepared by coating a subcoated cellulose acetate film base with a 4% aqueous gelatin solution. After this coating has dried, a coating is applied of a solution comprising 3 g. of 2-chloro-4-(4- diethylamino-2'-methylanilino)-5 -nitro-1-naphthol hydrochloride and 1% hypophosphorus acid in 33 cc. of

water. The photosensitive element is exposedandaliquid processing composition comprising; U T Sodium carboxymethyl cellulose "g-.. 4.5 Sodium hydroxide g 3.0 Metol g i Water 1 'i 100 is applied to the exposed photosensitive element as it is brought into superposed relationship with 'the image-re ceiving element. After an imbibition period of approximately one minute, the *imagereceiving'element is separated and contains a cyan positive dyeimageof-the photographed subject. k a Anexample'of the use of sulfite with a leuco dye, and given as an-illustration'only, is: 7

Example 3 1 Water cc Sodium carboxymethyl cellulose g 4.5 Sodium hydroxide g 2.0 Phenylethyl alcohol g 1.5 p-Anilino phenol g 0.2 Sodium suh'ite g 0.5

is applied to the exposed photosensitive element as it is brought into superposed relationship with the image-receiving element. After an imbibition period of approxi mately one minute, the image-receiving element is separated and contains a cyan positive dye image of the photographed subject.

It will be apparent that by appropriate selection of the image-receiving element from among suitable known opaque and transparent materials, it is possible to obtain either a colored positive reflection print or a colored posi tive transparency. Likewise, the inventive concepts herein set forth are adaptable for multicolor work by the use of special photographic materials, for example film materials of the type containing two or more photosensitized elements associated with a suitable number of image-receiving elements and adapted to be treated with one or more liquid processing compositons, appropriate developing agents suitable to impart the desired subtractive colors being incorporated in the photosensitized elements or in the liquid processing compositions. Examples of such photographic materials are disclosed in the previously mentioned US. Patent No. 2,647,049 to Edwin H. Land.

The inventive concepts herein set forth are also adaptable to the formation of colored images in accordance with the photographic products and processes disclosed and claimed in the copending application of Edwin H. Land, Serial No. 448,441, filed August 9, 1954, which is a continuation-impart of Serial No. 176,961, filed August 1, 1950, and now abandoned, and also those set forth in the copending application of Howard G. Rogers, Serial No. 748,421, filed July 14, 1958, which is a continuationin-part of Serial No. 415,073, filed March 9, 1954, and now abandoned.

U.S. Patent No. 1,102,028 to Rudolph Fischer, issued June 30, 1914, discloses the silver halide developing ability of leuco compounds such as those disclosed hereing, as well as the formation of a dye imageby these compounds. The photographic art, however, has generally considered the use of these compounds in color photography to be impractical and undesirable. It was therefore unexpected that these leucocompounds would be useful in obtaining a colored, positive image by a diffusion transfer process. such as described herein.

In those instances where the photographic art has referred to the use of these leuco compounds, it has been suggested that the presence of sulfite be avoided. See, for example History of Color Photography, Joseph -S. Friedman, American Photographic Publishing Co., Bo'ston, Mass., 1944, p. 374 5. It has been found, however, contrary to these suggestions, that it is not necessary to exclude sulfite-when using these leuco compounds, and small amounts of; sulfitei may be used,-particularly where they are employed in a difiusion transfer reversal proccess such as disclosed herein to obtain a positive dye image. k p

In the precedingportions of the specifications, the expression color has been frequently used. This" expres sion is intended to include the use of a plurality of colors to obtain black. p p

In employing the leuco compounds of this invention in film units suitable for use in self-developing cameras, such as the Polaroid Land Camera, sold by Polaroid Corporation, Cambridge, Massachusetts, the film unit may comprise a photosensitive element, an image-receiw ing element adapted to be superposed on said photosensitive element, and a-rupturable container holding a processing composition and adapted to release its contents for spreading over predetermined areas of said elements after rupture. Suitable structures of this type are described in the herein-mentioned vU.S. patents and patent applications. The leuco compound may be located in the processing composition or in a layer of the photosensitive element.

This application is in part a continuation of my copending US. application, Serial No. 464,175, filed October 22, 1954 (now abandoned).

Since certain changes may be made in the above processes without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description shall be interpreted as illustrativeand not in a limiting sense.

What is claimed is: r

1. In a process of forming photographic images in color, the steps which comprise developing a latent image contained in an exposed silver halide emulsion with an aqueous alkaline solution of a leuco compound of the formula:

wherein Y is selected from the group consisting of unsubstituted and substituted benzene and naphthalene rings containing a hydroxyl group in para position to the nitrogen to which Y is attached, each Z is selected from the group consisting of hydrogen, alkyl, amino and alkoxy radicals and each X is selected from the group consisting of hydrogen and alkyl radicals, to thereby provide in said emulsion a predetermined distribution of unoxidized leuco compound, transferring at least part of said distribution of unoxidized leuco compound by imbibition from said emulsion to an image-receiving layer in superposed relationship with said emulsion and oxidizing the diffused, transferred, unoxidized leuco compound to impart to said image-receiving layer a reversed, positive dye image of the developed image.

2. The process defined in claim 1 wherein said leuco compound is disposed, prior to exposure, in a photosensitive element comprising said exposed silver halide emulsion, and the solution containing said leuco compound is formed by permeating said photosensitive element with an aqueous alkaline liquid capable of solubilizing said leuco compound.

3. The process as defined in claim 2 wherein said leuco compound is present in the photosensitive element as an acid addition salt. t

4. The process as defined in claim 3 wherein said acid addition salt is the hydrochloride. 5. The process as defined in claim 2 wherein said liquid is introduced by being spread in a substantially uniform layer between said photosensitive element and said image-receiving layer as said photosensitive element and said image-receiving layer are brought into superposed relationship.

6. The process as defined in claim 2 wherein said liquid contains a thickener for'increasing viscosity and for facilitating the spreading thereof between said photosensitive element and said image-receiving layer.

7. The process as defined in claim 1 wherein said leuco compound is dissolved in an aqueous alkaline solution prior to application of said solution to said exposed emulsion.

8. The process as defined in claim 1 wherein the diffused, transferred, unoxidized. leuco compound is oxidized by exposure to air.

9. The process as definedin claim 1 wherein saiddifi fused, transferred; unoxidized leuco compound is-oxidized by an oxidizing agent incorporated in the image-receiving layer. 7 i

10; The process as defined in claim 1 whercinsaid aqueous alkaline solution contains a silver halide developing agent in addition to said leuco compound.

11. The process as defined in claim 2 wherein hypophosphorous acid is disposed with said leuco. compound in said photosensitive element.

12. The process as defined in claim 1 wherein said leuco compound is 2-chloro-4-(4fldicthylamino-2 methylanilino)-5-nitro-1-naphthol.

13. The process as defined in claim 1 wherein said leuco compound is 2-chloro-4-(4-diethylamino-anilinoy5- nitro-l-naphthol.

14. The process as defined in claim 1 wherein said leuco compound is 2-ch1oro-4-[4'-(N-ethyl-N-methylsulfonamidoethyl) -amino-2'-methoxyanilino] -1-naphthol.

15. The process as defined in claim 1 wherein said development is effected in the presence of an accelerating silver halide developing agent.

References Cited in the file of this patent V UNITED STATES PATENTS 1,102,028 Fischer June 30, 1914 2,206,126 Schinzel June 2, 1940 2,559,643 Land July 10, 1951 2,647,049 Land July 28, 1953 

1. IN A PROCESS OF FORMING PHOTOGRAPHIC IMAGES IN COLOR, THE STEPS WHICH COMPRISE DEVELOPING A LATENT IMAGE CONTAINED IN AN EXPOSED SILVER HALIDE EMULSION WITH AN AQUEOUS ALKALINE SOLUTION OF A LEUCO COMPOUND OF THE FORMULA: 